The present invention relates to catalysts for the oxi-chlorination of ethylene to 1,2-dichloroethane.
The catalyst that is generally used for oxi-chlorination of ethylene to 1,2-dichloroethane is constituted by cupric chloride supported on an inert porous oxide carrier such as alumina.
The catalyst is preferably used on a fixed bed.
In order to inhibit the reactions that lead to formation of byproducts such as ethyl chloride and carbon oxides, the cupric chloride is used in a mixture with promoters such as potassium chloride.
Mixtures of potassium chloride with cesium chloride have also been used in order to inhibit the formation of byproducts without having a negative effect on the catalytic activity (EP-A-62 320).
Known from DE 23 56 549 is a process for preparing 1,2-dichloroethane by oxi-chlorination of ethylene using a catalyst system obtained by impregnation of a carrier with an aqueous solution of CuCl2.3Cu(OH)2 and HCl, followed by heating, thereby CuCl2 is formed.
It has now been found unexpectedly that cupric oxychloride, Cu(OH)Cl, is a highly effective catalyst for the oxi-chlorination of ethylene to 1,2-dichloroethane, which provides a higher performance, in terms of selectivity and conversion, than cupric chloride or other copper compounds, such as cuprous chloride (CuCl) or cupric hydroxychloride of formula Cu2(OH)3Cl. The selectivity of the catalyst remains high even when working with high conversions.
The addition of promoters such as potassium chloride further improves the selectivity without reducing catalytic activity.
Potassium chloride can be used in a mixture with magnesium chloride and/or cesium chloride or other chlorides of the rare earths; it is used with a ratio of K/Cu to cupric oxychloride of 0.05:1 to 1.2:1.
Cupric oxychloride is prepared by oxidizing CuCl2 with air in the presence of moisture, working at room temperature or slightly above. In practice, the cupric chloride is left in contact with the humid air until conversion to Cu(OH)Cl occurs.
For use on a fixed bed, the cupric oxychloride is supported on porous inert oxides such as alumina.
Alumina is preferably used, or even more preferably mixtures of alumina with silica, containing more than 80% alumina by weight, are used.
It has in fact been found, and this constitutes another aspect of the invention, that the use of supports prepared from mixtures of boehmite with aluminum silicate allows to considerably improve the catalytic activity without reducing the selectivity of the catalyst.
The weight ratio between boehmite and aluminum silicate is preferably between 60:40 and 90:10.
The alumina that can be used as support generally has a surface area (BET) of more than 200 m2/g, preferably between 240 and 300 m2/g, and a porosity of 0.5-0.65 cm3/g; the volume of the pores with a radius of less than 50 A is 0.4-0.55 cm3/g.
Alumina/silica mixtures obtained from boehmite and from aluminum silicate have a surface area greater than alumina.
In the case of the support obtained from boehmite and from aluminum silicate in an 80:20 mixture by weight, the area is approximately 290 m2/g and porosity is 0.6 cm3/g.
The supported catalysts have surface area generally comprised from 130 to 200 m2/g.
Impregnation of the cupric oxychloride on the porous support is performed by using aqueous solutions of the oxychloride in an amount which is smaller than the volume of the pores of the substrate, for example equal to 90% of the volume.
The amount of oxychloride fixed on the substrate, expressed as copper, is comprised from 1 to 10% by weight, preferably 5-6%.
The support is in the form of granules whose geometric shape ranges from spherical to solid cylindrical to cylindrical with a through bore or bores to lobate cylindrical with through bores at the lobes.
Preferably, lobate cylindrical shapes with three or more lobes, with through bores having an axis which is substantially parallel to the axis of the granule and substantially equidistant and parallel with respect to each other, are used.
Granules having a three-lobed cross-section with through bores at the three lobes are preferred. The ratio between the surface and the volume of granules of this type of support is at least 2.4 cmxe2x88x921.
The height of the granules is comprised from 3 to 10 mm, preferably 4-7 mm.
The radius of the circumscribed circumference is from 2 to 5 mm.
Cylindrical granules with three or more lobes provided with through bores are described in EP-B-591 572, the description of which is included herein by reference.
The lobate and perforated granules are preferably prepared by compression tableting, using lubricant applied to the surface of the mold and punches.
Solid lubricants, such as magnesium stearate and stearic acid, are preferably used.
The use of catalysts in the form of cylindrical granules having lobes and through bores allows to significantly reduce pressure load losses and to improve the catalytic activity and selectivity.
By using the catalysts in their lobate and perforated forms, it is also possible to conduct the oxi-chlorination reaction in a single stage instead of three, as normally occurs when using catalysts having a solid cylindrical shape.
For single-stage operation, a large excess of ethylene with respect to the hydrochloric acid is used. This allows to improve the reaction selectivity by virtue of the high specific heat of ethylene.
The reactor that can be used is generally of the tubular type formed by a bundle of tubes which have a diameter between 20 and 40 mm and are connected to each other and to a cooling jacket.
The gaseous mixture comprising ethylene, hydrochloric acid and air or oxygen is fed from below toward the top of the reactor.
The temperature of the reaction is generally between 210xc2x0 and 350xc2x0 C., with residence times between 1 and 6 seconds.
The loading of the catalyst in the reactor, in the case of the single-stage process, is performed in a plurality of layers, with a catalytic mass concentration profile which increases from the bottom upwards.
In the case of the three-stage process, the reactor of the third stage works with the highest concentration of catalyst.
The following examples are given to illustrate but not to limit the invention.